Back here at home that mystery at the Brooklyn bridge. There is the bridge this morning as authorities try to figure out who scaled the world famous landmark and replaced American flags with white flags. ABC's linsey Davis is there for us right now with the latest. Good morning, linsey. Reporter: Good morning, robin. Just to give you a sense talking about 120,000 cars, 4 Thu thousand pedestrians, 3100 bikes that cross the Brooklyn bridge every day. It has been targeted by terrorists before. And while terrorism has been ruled out in this instance it's raised numerous questions about security. This morning, a serious investigation into how and why two enormous American flags atop the famed Brooklyn bridge were swapped for a pair of old glories apparently bleached white. We don't take these things lightly or as a joke. Reporter: Take a look at this Earth cam video at 3:30 the light illuminating one of the flags flickers out. 12 minutes later the same thing with the other flag, watch again. The flag there one moment, gone the next. At 5:30 A.M., construction workers notice the flag flip-flop. Officers soon make their way up the bridge's main cables and find these aluminum pans secured with zip ties covering those lights. They then replace the white flags folding them into tight triangles following traditional procedure, but the mystery persists. That is a matter of concern. I am not particularly happy about the event. Reporter: Police are now looking for five people seen crossing the bridge about 20 minutes before that first light went out. They say whoever pulled off the elaborate breach was able to scale 276 feet, somehow making it past the locked Gates that sit atop the steel cables. There's some indication of some good deal of preoperational planning, perhaps some indication that they have experience climbing in construction or in bridgework or that they may have actually been up there before. Reporter: This morning, the NYPD has ruled out terrorism as other theories abound. Perhaps an elaborate art installation or eye political statement about surrender. Brooklyn borough president Adams now offering $5,000 for information leading to an arrest. This is the Brooklyn bridge and the only person that should be surrendering at this time is the person who's responsible for the desecration of this flag. Reporter: Police are calling it a case of trespassing, malicious mischief and reckless endangerment but could have been far worse. It certainly could have been, linsey, thank you. The very least a frightening security breach.

This transcript has been automatically generated and may not be 100% accurate.

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